Antenna is an essential component in wireless communications and the coverage area of the signal from an antenna is characterized by the antenna radiation pattern. In general, an antenna radiation pattern covers a designated beamwidth region as well as some beamwidth region outside the designated beamwidth region. Since the gain of the antenna radiation pattern outside the designated beamwidth region does not promptly reduce to a negligible level, the data transmitted from a transmitter to a receiver will partially leak to the beamwidth region outside the designated beamwidth region to be received by undesired users. Consequently, the undesired users may obtain the data with higher error probability.
To solve the above problem, spot beam antenna, first appeared in 1993, can highly concentrate the radiated energy within the designated beamwidth region so as to exclude the users outside the designated beamwidth region from receiving the signals. However, physical antenna designs are needed to achieve the desired performance. When the required beamwidth is narrow, elaborate designs on antenna components, such as feeder systems, structure of reflectors, and aperture distributions, are extremely expensive in practice. Besides, the beamwidth is also difficult to be adjusted physically.